The field of the present invention is apparatus and methods for producing heat exchange with and assisting flow of a body fluid in a body conduit of a patient.
Intra-aortic balloon pump (IABP) catheters are used to assist a patient's heart in pumping blood through a patient's circulatory system. IABP catheters typically may be used in situations in which the pumping function of a patient's heart is impaired, and particularly during and/or following heart surgery.
An IABP catheter typically has an inflatable balloon at its distal end. The catheter is inserted into the patient's central venous system so that the balloon is located adjacent the patient's heart. The balloon is then inflated and deflated cyclically, and preferably in timing with the patient's heartbeat. As the balloon inflates and deflates, it provides a pumping function to help move blood through the patient's circulatory system.
In addition to using an IABP catheter to assist in pumping blood when a patient's heart function is impaired, it may be desirable to reduce the patient's body temperature below normal body temperature so that the patient experiences hypothermia. Many advantages of hypothermia are known. By way of example, it has been found desirable to lower body temperature to reduce the metabolism of the body. This has been particularly desirable in surgical applications where the reduced metabolism has made it possible to more easily accommodate lengthy operative procedures. In cases of stroke and several other pathological conditions, hypothermia also reduces the permeability of the blood/brain barrier. It inhibits release of damaging neurotransmitters and also inhibits calcium-mediated effects. Hypothermia also inhibits brain edema and lowers intracranial pressure. In the case of cardiac arrest, application of hypothermia has been shown to reduce myocardiac infarction as well as prevent or limit neurologic injury. Hypothermia has also been used during cardiac surgery with cardiopulmonary bypass as a means to protect the brain from ischemic injury. In other cases, it may be desireable to cool a patient experiencing a fever so that the patient's body temperature returns to normal.
In yet other situations, it may be desirable to raise the patient's body temperature. Such situations may occur once the application of hypothermia is no longer needed and it becomes desirous to warm the patient back to normal temperature. In another application, warming the patient may be needed if a patient's body drifts dangerously close to severe hypothermia. Control of a patient's temperature may be problematic during hospital stays and particularly during active interventions such as surgery. The patient's body temperature may drift too low during surgery, potentially being deterimental to the patient's health. Body temperature may be artificially maintained at a normothermic temperature (approximately 98.6° F.) during surgery and post-operatively.
Conventional therapies used to manage patient temperature include acetaminophen (Tylenol), cooling blankets, heating blankets such as warm water blankets, forced warm or cool air, heat lamps, endovascular catheters, ice packs, ice baths, cold or warm infusions, and cold saline rectal or gastric lavages. With some of the conventional therapies, the warming or cooling rates are restricted by the body's ability to resist surface cooling or heating with vasodilation and sweating. The conventional approaches to cooling a patient also may require additional steps, may require excessive time and may not provide for precise control of patient temperature over long periods of time. Further, some of these devices cover a significant portion of a patient's body, inhibiting access to the patient.
Other techniques for controlling patient temperature employ intravascular heat exchange catheters that may be inserted into the patient's circulatory system. A relatively cool or warm fluid may be circulated through such catheters in a closed loop and exchange heat with blood flowing in the circulatory system, and may improve the patient's medical outcome. Carrying out both the pumping function of an IABP catheter and the heat transfer function of a heat exchange catheter conventionally requires the use of two separate catheters. Compared with using a single catheter, using two catheters increases the complexity of the procedure and requires additional steps to be carried out.